Both endogenous and exogenous lactate is essential for the activation of certain enzymes such as matrix metalloproteinases, as well as for regulation of the expression of oncogenes (Myc, Ras), transcription factors (HIF-1, E2F1), tumor suppressors (BRCA1, BRCA2), and cell cycle genes, as shown in MCF-7 breast cancer [126]. Here, HIF1A is linked to breast cancer.